The present invention relates to a method and apparatus for securing sheet metal to rigid plastic. The invention is useful, as one example, for securing metal portions of picnic cooler side walls to the lower plastic portion of the cooler case.
In the construction of better picnic coolers, sheet metal is used as a covering material because of its strength and durability. Semi-rigid foam plastic is used as an insulating material in the walls of the cooler. Rigid plastic is used for the base covering. Problems have been experienced in foaming the insulation in place, and one construction uses a pre-formed rigid plastic base, which must be secured to the metal cooler base during manufacture. In the past, the metal and plastic portions of the case side walls were secured together by forming a groove in the metal portion prior to foaming. Tape was also used, so that after the foaming operation, the plastic foam expanded into the groove in the metal, and the combination of this mechanical coupling and the tape held the side wall to the base.
In some cases, during the foaming process, excess pressure might be generated which would pull the plastic base and metal wall sections apart, and thereby cause a reject.
According to the present invention, a cooler base is pre-formed of high density plastic, such as polyethylene, and it includes short upright side wall portions which partially overlap the cooler metal side walls. The metal cooler side walls are assembled to the plastic base, the lower portion of the metal side walls being formd with a groove to receive the top edge of the base. The metal side walls are secured to the plastic base by means of a hand tool which includes a pair of oppositely-directed punch heads coupled to a pneumatic cylinder and piston rod unit by an expansion linkage. The tool is aligned with the interface beween the metal and plastic, and the punch heads are spaced slightly inwardly from opposite side walls of the cooler prior to operation of the tool.
To actuate the tool, the operator pushes a lever with his finger, and this coupled pressurized air to the cylinder and piston rod unit which, in turn, when actuated, causes the linkage to expand, thereby driving the punch heads apart. Each punch head is provided with a tri-facial point for forming a detent in the metal adjacent the plastic. Part of the metal is torn at the detent and embedded in the plastic to couple the two elements together. When the lever is released, air is routed to reverse the action of the cylinder and piston rod units and retract the expansion linkage, thereby withdrawing the punch heads from the metal. The cooler can then be assembled, and the side insulation foamed in place.
The present invention eliminates the need for tape previously used in the manufacture of picnic coolers, and has been found to provide a better connection between the metal and plastic base of the cooler so that during subsequent foaming, the plastic base does not separate from the metal side walls.
Persons skilled in the art will be able to understand further features and advantages of the present invention from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will be used to refer to like parts in the apparatus.